Pentode tube



W. L. KRAHL ug. E932.

PENTODE TUBE Filed May 6. 1950 2 Sheets-Sheet Aug- 2, 1932 w. 1 KRAHL 1,869,568

PENTODE TUBE y Filed May 6, 1930 2 Shees-Shee 2 VII/IIA 46 e 48 @f6 45 Z5 4 .H/mi 40 ZZ Fille/17111 l IIE 43 I 63 44 INVENTOR 50 ML75@ z.. KRAHL A ORN EY Patented Aug. 2, 1932 UNITED STATES PATENT OFFICE WALTER LOUIS KRAHI., OF MONTCLAIR, NEW JERSEY, ASSIGNOR T0 ARCTURUS RADIO TUBE COMPANY, OF NEWARK, NEW JERSEY, A CORPORATION OF DELAWARE PENTODE TUBE Application led May 6, 1930. Serial No. 450,076.

This invention relates to electron devices and particularly to such devices commonly called vacuum tubes in which an electron stream flowing between a cathode and anode is influenced by a control electrode or grid.

O ne of the objects of the invention is to increase the eliiciency of such an electron device.

Another object of the invention is to eliminate or reduce to a minimum the space charge between the cathode and anode so as to permit a freer flow of the electron stream.

Another object of the invention is to provide a means in an electron device to reduce to a minimum the emission of electrons from the anode, called secondary emission.

Another object of the invention is to provide a structure for an electron device in which all of the elements may be supported rigidly and insulatedly with respect to each other.

Other objects of the invention and objects relating particularly to means and methods of constructing and assembling the various parts will be apparent as the description of the invention proceeds.

One embodiment of the invention has been illustrated in the accompanying drawings in which: l

Fig. 1 is a sectional front elevation of my improved pentode or live element tube;

Fig. 2 is a plan view of the elements as shown in Fig. 1;

Fig. 3 is a sectional plan view taken on the line 3 3 of Fig. l;

Fig. 4 is a sectional plan view taken on the line 4-4 of Fig. 1

Fig. 5 is a sectional side view taken on the line 5-5 of Fig. l;

Fig. 6 is a detailed sectional side view taken on the line 6--6 of Fig. 1 and showing a 'clip for securing the filamentary cathode;

and

Fig. 7 is another detailed side view taken on the line 7--7 of Fig. 1 showing the means to secure the end of the cathode.

Referring now more specifically to the drawings the invention is shown as comprising a glass envelope 10 mounted on the usual base 11 which contains the terminals for making the necessary electrical connection for the tube. A stem 12 is formed integral with the envelope 10 and extends upwardly within the envelope terminating in a press 13 in which the various support wires for the elements are sealed, these wires forming the electrical connection between the elements and the termlnals at the base ofthe tube.

The elements are mounted as a unitary structure which may be assembled entirely independently of the press 13 and support wires. To this end the anode 14 is formed of a palr of plates bent channel-shaped as indicated in Fig. 3 with a flat central portion 15 and angular side portions 1G provided with parallel outwardly extending flanges 17 which are adapted to be against the ianges of the opposite plate so that the two plates cooperate to form a flat tubular structure. Longitudinal grooves 18 may be provided in the cooperating faces of the flanges 17 to form sockets to receive support posts to be hereinafter described.

The upper and lower ends of the side mem- !bers 16 may be extended to form arms 19 which are provided with reduced ends forming shoulders 20 and lingers 21.

At the top and bottom of this anode structure are provided insulating plates 22 and 23 respectively made of mica, isolantite, crolite, or other desirable insulating material which will stand a high temperature and is capable of being degasiied. These insulating plates 22 and 23 may be made exactly alike, if desired, and each may be provided at each end thereof with an'opening 24 to receive the two fingers 21, one on each portion of the anode. The outer edge of the opening 24 is made to conform with the side members 16 of the anode portion so that when the fingers 24 are bent over the opposite side of the insulating plate they will lie against the edge thereof. The iingers 21 pass through the opening 24 in each plate and are bent as indicated so that the plates are held firmly upon the shoulders 2O at each end of the anode and are thereby maintained in spaced relation with respect to the anode and the other elements. v

Each of the openings 24 has a rounded notch 25 on its inner side on the axis of the plate and a pair of support rods 26 extend, one through each pair of opposing openings 24 and lie in the notches 25.- These support rods 26 have woundvaround them a helical grid 27 which is wound to conform with the general outline of the anode structure and adapted to be positioned close to it. This grid forms a means to prevent secondary emission from the anode structure.

Spaced a short distance inwardly from the notch 25 on each of the insulators 22 and 23 is positioned a pair of holes 28 lying on the axis of the insulator. A second grid 29 helically wound upon two support rods 30 and 31 is positioned inside of the grid 27 and 1s adapted to conform to the outline thereof but is spaced a short distance inwardly. The rods 30 and 31 extend through the opposed openings 28 in the insulator plates 22 and 23 which tend to anchor them against transverse movement. This grid functions to reduce the space charge between the anode and cathode.

Inside of the grid 29 is a third grid 32 formed of a helix of wire wound upon two parallel support rods 33 and 34 which are adapted to pass through a pair of holes 35 which are placed on the axis of each of the insulators 22 and 23 and arc spaced slightly inwardly from the holes 28. This grid forms the third or inner grid, which is the control electrode of the device.

At the exact center of each insulating plate I provide a hole 36k and spaced on each side of this hole I provide holes 37 and 38, these holes being used solely in the upper insulator 22. Also on each insulator I provide three spaced apart notches 39, 40, and 41 on one side or edge while corresponding oppositely positioned notches 42, 43, and 44 are provided in the opposite edge. These notches are used solely on the lower insulator. A metal strap 45 is placed around the lower insulator 23 and engages the notches 39 and 42 at the side thereof. This strap falls just inside of the hole 35 for supporting the inner grid. The ends of the strap 45 are brought together beneath the insulator 23 and are adapted to be welded or otherwise secured upon opposite sides of a. support rod. In like manner a strap 46 is bent around the insulator plate 23 and engages the notches 40 and 43 at the center of the plate, the lower ends of the strap being brought together on each side of a second support rod. Also a strap 47 is provided bent around the insulator 23 and engages the notches 41 and 44 and has its ends brought together underneath on opposite sides of a third support rod.

An M-shaped filament has one free end i welded under the strap 45 at the center thereof as indicated and passes upwardly toward the insulating plate 22 to a point adjacent y lators.

the plate where it is bent downwardly, pass' ing under the strap 46, and upwardly a ain toward the insulating plate 22, being ent downwardly again at a point adjacent the plate to have its other free end welded beneath the metal strap 47 on the lower insulating plate. This anchors the lower end of the filamentary cathode.

In order to support the two upper loop ends of the cathode, I provide two s irally wound springs 49 and 51 which are adapted to rest upon the top of the insulating plate 22 and which have their upper ends passing downwardly through the center of the spiral and through the holes 37 and 38 in the plate, terminating in hooks 50 and 52 over which the two loops of the filament pass.

From this description it will be seen that the elements of the tube, namely the anode, outer grid, control grid, and inner grid, and also the tilamentary cathode are supported between the insulating` plates 22 and 23 inv spaced relation to each other. Movement of the various elements transversely of the insulating plate is prevented by this construction but in order to prevent any longitudinal movement of the various elements, especially the three grids, which might perhaps cause microphonic noises in the tube I provide clips for securing certain of the grid support posts to the insulating plates or to one ot' them. Thus one of the support rods 26 has welded to it the ends 53 of a clip 54 which is bent U-shaped and passes over theedge of the insulating plate. This se curely holds the post 26 Vagainst any longitudinal movement with respect to the insu- Likewise the support rod 31 which forms one of the supports for the middle grid 29 is provided at'its lower end with a clip 55 exactly similar to the clip 54 already described. Also the rod 33 forming one of the supports for the inner grid 32 is provided at its lower end with a similar clip 56 which secures the rod 33 against longitudinal movement.

In order to mount the unitary element structure already described in the vacuum tube a pair of heavy support rods 57 are provided in opposite ends of the press 13. These rods are bent outwardly and then upwardly lying parallel to each other andy spaced apart so as to engage with the grooves 18 of the anode structure. The unitary element structure is then held with the upper ends of the posts 57 cooperating with the grooves 18 and then the whole structure is slip ed downwardly, the posts sliding within-t e grooves 18 until it reaches a predetermined distance from the press 13 whereupon the flanges 17 are welded to the posts 57 thereby rigidly securing the anode, as well as thewhole structure, to the posts. The middle grid post 30 is made slightly longer than the post 31 and extends downwardly a short distance further below the under surface of the insulator 23. A curved support post 58 is sealed in the press 13 adjacent the post 57 and is bent outwardly so that it crosses the lower end of the post 30 to which it may be welded thus forming an additional support for the whole structure as well as an electrical connectlon for the middle grid. Another support 59 sealed in the press 13 extends upwardly and is bent outwardly so that its end comes between the two ends of the strap 45 which is then welded to it which thereby makes an additional support for the whole unit and an electrical connection is made for one end of the filament 48. At the center of the press 13 is provided lanother support rod 60 which may be made perfectly stralght which extends upwardly between the two ends of the strap 46 to which it may be welded, thereby forming still another support for the element structure. Adjacent the support. 60 is another support 61 sealed in the ress 13 and corresponding to the support 59 ut bent in the opposite direction and positioned between the ends of the strap 47 to which it may be Welded thus forming the electrical connection for the other end of the filament 48 and an 'additional supporting means for the structure. The support rod 34 for the inner grid 32 is preferably made somewhat longer than its corresponding support 33 and extends downwardly below the insulator 23 so that it may be welded to a support rod 62 sealed in the press between the extreme right hand support rod 57 and the filament con- ,nector support 6l.

The purpose of the outer grid in the tube is to prevent secondary electron emission from the anode. When electrons from the cathode strike the anode they tend to liberate other electrons which tend to pass out into the space between the anode and cathode. However, if the grid which is adJacent the anode is supplied with a negative charge any electrons sent out from the anode will be repolled and will turn back against the anode again. It is, therefore, necessary or desirable to place a negative charge on the outer grid. This may be done by connecting directly to the cathode which has a negative or neutral charge as it is connected to the negative side of the B battery. Where alternating current is used the mid-point of the filament is chosen for this point of connection as this represents the average potential of the lilamentary cathode and hence I 'provide a strap 63 which is bent channel-shaped as shown in Fig. 4 to avoid the other support posts and has its ends welded to the support post 26, which is not provided with the clip 54, and the strap 46 which is connected to the center of the filament cathode 48.

From the above description and from an inspection of the drawings it will be evident that all of the six grid supporting posts 26,

30, 31, 33, and 34 are either secured to the lower insulating plates by means of the cli 54, 56, or 55, or the strap 63, or are attached to support rods which are sealed in the press so that they are all prevented from longitudinal movement and microplionic noises are thereby reduced or entirely eliminated.

The grid connecting and supporting post 58 may be connected by means of a wire 64 to a grid terminal 65 mounted on the base 11 of the tube; also one endof the filament may be connected to the filament support post 59 by means of the wire 66 through the filament contact terminal 67 at the base of the tube and the other end of the filament which' is attached to the support rod 6l may be connected by means of a wire 68 to the other lament contact terminal 69. The support rod 58 which is welded to the middle grid support post 30 may be connected by means of a Wire 64 to a shield grid contact terminal 65 and one of the anode supporting posts 57 may be connected, as shown, by means of a wire 72 to the anode contact terminal 73 at the base of the tube.

The middle grid 29 is adapted to prevent space charge similarly to the shield grid in a shield grid tube and hence is preferably supplied with a positive potential greater than that of the cathode and less or equal that of the anode. Accordingly t-he connection to the positive terminal of a battery may be made by mea-ns of contact terminal 65.

While ive terminals have been shown on the tube and indicated as falling in a straight line it is evident that these terminals may be arranged in any desirable manner as in a circle to fit a standard live terminal vacuum tube socket.

It will be evident from the above description that I have provided a live element or pentode tube in which all of the elements are spaced from each other and held so spaced in a rigid position with special means provided to prevent any longitudinal movement of the elements so as to cause microphonic noises or other disadvantageous results.

Many modifications may be resorted to 4without departing from the spirit of the invention and I do not, therefore, desire to limit myself to what has been shown and described except as such limitations occur in the appended claims.

What I claim is:

1. In an electron device a pair of spaced apart insulators, a, plurality of helically wound grids spaced between said insulators, a pair of support rods for each of said grids, means to rigidly anchor one of each pair of support rods upon said insulating members, and means to rigidly anchor the other of each pair of support rods to the press of said tube.

2. In an electron device a tubular anode, any insulator rigidly held at each end of said anode, a grid formed of helically wound wire mounted on a pair of support rods extending between said insulators, said rods passlng through openings in said insulators, a secy ond helically wound grid within said irst mentioned grid, a pair of support rods for said second grid extending through openings in said insulators, a third helically wound grid within said second mentioned grid, a pair of support rods for said third grid, said rods extending through openings in said insulators, and means to anchor said support rods to said insulators.

3. In an electron device a lat tubular anode, an insulating plate secured across each end of said anode, a helically wound flattened grid within said anode and adjacent to it,a pair of supporting rods for said grid extend ing through openings in said insulating plates, a second helically wound flattened grid within said first mentioned grid, a pair of supporting rods for said second grid extending through openings in said plates, a third helically wound flattened grid within said second grid, a support rod for said third grid extending through openings in said insulating plates, a ilamentary cathode within said third grid, means to support said cathode in spaced relation between said insulating plates, and means to anchor each of said support rods to one of said insulating plates.

4. In an electron device a press, a pair of support rods extending upwardly from said press, a attened tubular anode attached t0 said support rods, a pair of insulating plates positioned one on each end of said anode, a helieally wound grid within said anode, a pair of supporting rods for said grid extending through openings in said insulating l plates, a support rod sealed in said press and secured to said last mentioned support rod, a second helically wound grid within said irst mentioned grid, a pair of .supporting rods for said second grid extending through openings in said insulating plates, a support rod secured in said press and attached to said last mentioned support rod, a third grid between said first mentioned grid and said anode, a support rod for said grid extending through openings in said plate, and a support rod sealed in said press and secured to said last mentioned support rod, and means to connect said third grid to said cathode.

In testimony whereof I aix my signature.

WALTER LOUIS KRAIIL. 

